There are a number of refreshing points about this parliament. The fact that it has seen the most rebellious Conservative parliamentary party for many decades, for example, or the fact it is giving more power to backbenchers to question members of the executive.

There is one trend which is perhaps a little more worrying. This parliament has already seen the most by-elections for reasons other than death/ill-health or what could loosely be described as "scandal", since the parliament that followed the October 1974 general election.

So far – and it's worth repeating that we're not even half way through this parliament – we've had six by-elections caused, or set to be caused, by MPs resigning to concentrate on other roles. Labour MP Sir Peter Soulsby resigned to win election as the Mayor of Leicester, Gerry Adams resigned to win election in a foreign country, Martin McGuinness resigned to concentrate on his role as Deputy First Minister of Northern Ireland, Labour MPs Tony Lloyd and Alun Michael resigned to contest Police and Crime Commissioner elections later this year, and many readers will be familiar with Louise Mensch's recent decision to stand down and spend more time with her family.

The other by-elections so far have been caused by Labour MPs Eric Illsley and Phil Woolas resigning early last year for false accounting and false statements during an election campaign respectively, and the sad deaths of Labour MPs David Cairns, Alan Keen and Marsha Singh. In the 2005-10 parliament, only two MPs resigned to concentrate on other duties: Tony Blair and Boris Johnson. I have listed below the number of MPs who resigned for similar reasons in each parliament (I have excluded by-elections caused by an MP seeking to fight his own seat, such as the fifteen Unionist MPs who sought re-election in opposition to the Anglo-Irish Agreement in 1986):

2001-05: 2

1997-01: 5

1992-97: 2

1987-92: 4

1983-87: 5

1979-83: 2

1974 (Oct)-79: 10

1974 (Feb): 1

1970-74: 9

1966-70: 5

1964-66: 5

1959-64: 32

1955-59: 16

1951-55: 16

1950-51: 4

1945-50: 20

Clearly the six by-elections in this parliament look rather small compared to the 32 in the 1959-64 parliament, or the 20 in the 1945-50 parliament. What explains these high figures? In those parliaments, and indeed most parliaments before the 1970s, many of the by-elections were caused by MPs being awarded life peerages. This happens rarely now – Betty Boothroyd was the last MP to leave the Commons by being sent straight to the Lords. Even more were caused by MPs of both parties succeeding to hereditary peerages.

However, peerages alone do not explain the previously high figures. There were also several resignations to take up positions that now seem archaic, or odd for an MP to occupy. Amongst my favourites are: Chairman of the West Midlands Coal Board, the Northern Ireland Government Agent in London, Governor of Bombay, Recorder of Manchester, High Commissioner to Rhodesia, Director of the International Institute for Labour Studies in Geneva, and Chairman of the Horserace Betting Levy Board. Another noticeable change is that MPs are no longer routinely appointed high court judges – perhaps showing how focused modern MPs are on political careers and political careers alone.

In the post-1979 era, MPs seem a lot less likely to resign to take up another position. Whereas in previous years they might have resigned to pursue a media career, or to chair a quango, they are generally more likely to take up higher profile positions, such as in diplomacy. This is also reflective of the relatively recent trend of career politicians, who are unwilling to leave Parliament.

The fact that six have left so far in this parliament could be seen as a good thing or a bad thing. You might perceive the change to be as a result of our political class being a little less careerist and more willing to take up executive positions outside Parliament. Alternatively, you might think it shows that Parliament is less worthwhile or prestigious. Either way, we can expect a rise in the number of MPs looking for alternative employment – voluntarily.